Despite billions in research dollars and a vow to improve their handling of this war’s “signature wound,” the military’s ability to diagnose troops with traumatic brain injuries, or TBIs, is “about as reliable as a coin flip.”

That’s only one of the disturbing findings of a new investigation by ProPublica and NPR. According to the Pentagon, 11,500 troops are suffering from TBIs. But the investigation, which pored over unpublished military documents, studies and correspondence between military officials and troops, concluded that the figure is likely higher — by tens of thousands.

The investigation is the latest in a series of reported failings in care for ailing vets, as well as TBI diagnosis and treatment. But it comes three years after the Pentagon vowed to improve the management of brain injuries, and poured $1.7 billion into doing just that.

Since then, at least some of that money has gone into a handful of out-there research efforts, including brain implants and helmet sensors. But outside the science lab, progress has been agonizingly slow: One of the military’s TBI diagnostic tests missed the injuries in 40 percent of troops, according to an unpublished study cited by the report. And much-touted handheld devices, meant to spot TBIs in the war zone, often fail to transfer the information to a troop’s permanent medical file. Not that paper records fare much better. They’ve often “been lost, burned or abandoned in warehouses.”

And while the military’s three-phase TBI screening exam sounds thorough (troops are screened before, during and after deployment), each test is fundamentally flawed, to the extent that soldiers admit to “gaming” the exam by memorizing the right answers. In an e-mail to the report’s authors, an unnamed military official described the tests as “coarse, high-level screening tools that are often applied in a suboptimal assembly line manner with little privacy” and “huge time constraints.”

But the workings of the brain remain largely a mystery, so it makes sense that TBIs would too. The injuries are difficult to diagnose and adequately treat, because experts aren’t entirely sure how they happen. But military docs are ignoring sanctioned tactics, like restricting activity among TBI patients to prevent further damage. Other troops are prescribed psychotropic drugs, rather than enrolled in cognitive therapy, which is the approach recommended by a panel of Pentagon-backed health experts.

Top military brass aren’t offering many specific solutions, other than a “cutting edge” medical facility set to open later this year. But Lt. Gen. Eric Schoomaker, the Army’s surgeon general, acknowledged that an adequate handling of TBIs continued to elude them.

“We still have a big problem and I readily admit it,” he said. “That is a black hole of information that we need to have closed.”